This project determines the short term and long term effective stiffness values for Cross Laminated Timber (CLT) with a reinforced concrete topping. The reinforced concrete was attached to the CLT panels with interface connections, and different types of interface connections were tested. Throughout this project, there are 31 tests with composite CLT floor panels. Described in this report are:• Eight 2 ft. by 10 ft. 8 inch composite floor panels with different interface shear connections. All these 2 ft. by 10 ft. 8 inch panels were tested to failure in positive bending moment under simply-supported conditions.• Three 8 ft. by 8 ft. composite floor panels with inclined self-tapping screws. The panels were tested to estimate the initial stiffness in strong and weak axis bending, under positive and negative bending moments. In addition, two-way bending flexural (warping) stiffness values were obtained from testing results. Lastly, the floor panels were tested to failure under weak-axis direction, positive moment bending, and in strong and weak axis bending under negative moment bending.• One 37.5 ft. long by 8 ft. test specimen with inclined self-tapping screws was tested to failure.• One 20 ft. by 4 ft. specimen and one 13.5 ft. by 4 ft. specimen under positive and negative bending moment, respectively, tested under creep loading.These tests aided in the determination of effective stiffness values that can be used for design of floor panels that have a total thickness of 9 inches, including a 2-1 4 inch concrete lamina, over a five-ply CLT panel. In addition, estimates of failure loads and moments presented in this thesis provide information needed for future structural designs of the CLT concrete composite floor systems.